Spin-leakage of the fullerene shell of endometallofullerenes: EPR, ENDOR and NMR evidences

Abstract

On embedding in the poly(bisphenol A carbonate) film, the lanthanum paramagnetic endometallofullerene, La-EMF, has featured stability against oxygen for more than 1 year's storage of the film on air. Furthermore, an intense H-ENDOR signal was discovered in this system. Since there are no protons in La-EMF, the matrix H-ENDOR testifies permeability of the fullerene shell for the electron spin density. The EPR signals of La-EMF with unusually small hyperfine splitting constants a La which were revealed in DMF and some other polar solvents, also suggest the partial transfer of the unpaired electron outside the fullerene cage. Moreover, for liquid solutions of La-EMF in hexamethylphosphoramide (HMPA), molecules of which contain the NMR active phosphorus-31, the paramagnetic shift of the 31P NMR signal of bulk HMPA molecules in the presence of La-EMF was revealed. Thus, the area of localization of the unpaired electron is not restricted by the fullerene shell but a runoff of the electron spin density beyond the fullerene cage takes place. The spin-leakage of the fullerene shell is worth consideration in sight of possible applications of fullerenes as the basis of novel magnetic materials.